<?php
/**
 * Turning a dead path back into a live URL.
 *
 * @package Adminkeep
 */

namespace Adminkeep\Service;

defined( 'ABSPATH' ) || exit;

/**
 * Resolves a recorded old path to the post's current address.
 *
 * The target is resolved live, from the post id, every time. That is what makes redirect chains
 * a non-problem: if a page moved A to B and later B to C, both rows point at the same post, and
 * both resolve straight to C in one hop. There is no chain to flatten and no cycle to detect,
 * because a chain is never built in the first place.
 */
class PathRedirectResolver {

	/**
	 * The current URL for a path that no longer resolves.
	 *
	 * @param string $path Requested path.
	 * @return string|null Absolute URL, or null if nothing should happen.
	 */
	public static function resolve( $path ) {
		$post_id = PathRedirectStore::lookup( $path );

		if ( null === $post_id ) {
			return null;
		}

		$post = get_post( $post_id );

		if ( ! $post instanceof \WP_Post ) {
			return null;
		}

		// A trashed or unpublished target stops redirecting. Sending a visitor to a 404 with a
		// 301 in front of it is worse than the 404 alone: the 301 is cached and the mistake
		// outlives the fix.
		//
		// Attachments are the exception on both counts. They live at post_status 'inherit', not
		// 'publish', and the row recorded for one points at a *file* that moved — so the target
		// is the file URL, never the attachment page nobody asked for.
		if ( 'attachment' === $post->post_type ) {
			if ( 'inherit' !== $post->post_status ) {
				return null;
			}

			$permalink = wp_get_attachment_url( $post->ID );
		} else {
			if ( 'publish' !== $post->post_status ) {
				return null;
			}

			$permalink = get_permalink( $post );
		}

		if ( ! is_string( $permalink ) || '' === $permalink ) {
			return null;
		}

		// The page moved back to the address being requested. Redirecting would loop.
		if ( PathRedirectStore::normalise( self::path_of( $permalink ) ) === PathRedirectStore::normalise( $path ) ) {
			return null;
		}

		return $permalink;
	}

	/**
	 * The site-relative path of a URL.
	 *
	 * @param string $url Absolute or relative URL.
	 * @return string
	 */
	public static function path_of( $url ) {
		$path = (string) wp_parse_url( $url, PHP_URL_PATH );
		$base = (string) wp_parse_url( home_url( '/' ), PHP_URL_PATH );

		// Subdirectory installs: the request carries the subdirectory, stored paths never do.
		if ( '' !== $base && '/' !== $base && 0 === strpos( $path, $base ) ) {
			$path = substr( $path, strlen( $base ) );
		}

		return PathRedirectStore::normalise( $path );
	}

	/**
	 * The path the visitor actually asked for.
	 *
	 * @return string
	 */
	public static function requested_path() {
		if ( empty( $_SERVER['REQUEST_URI'] ) ) {
			return '';
		}

		return self::path_of( esc_url_raw( wp_unslash( $_SERVER['REQUEST_URI'] ) ) );
	}
}